Helmet



FIG. 1 is a top, rear, left side perspective view of a helmet according to our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a right side elevational view thereof, the left side elevational view being a mirror image of FIG. 6.

The broken lines represent portions of the helmet that form no part of the claimed design. 

CLAIM The ornamental design for a helmet, as shown and described. 